Geomagnetic storms may influence risk of stroke

NEW YORK (Reuters Health) - More strokes happen when
geomagnetic storms are afoot, according to a new review of
stroke literature - although it's not clear what protective
measures anyone could take, researchers said.

Geomagnetic storms happen when the Earth's magnetic field is
disturbed by solar winds or coronal mass ejections, which throw
out powerful magnetic fields from the sun.

Among more than 11,000 people who had a stroke, the event
was almost 20 percent more likely to happen on days with
geomagnetic storms, researchers in New Zealand found.

"The results were a big surprise to us," said lead author
Dr. Valery L. Feigin of the National Institute for Stroke and
Applied Neurosciences at the School of Rehabilitation and
Occupation Studies at Auckland University of Technology.

"What we were particularly surprised with was the size and
consistency of the effect of geomagnetic storms on the risk of
stroke occurrence, suggesting that geomagnetic storms are
significant risk factors for stroke," Feigin told Reuters Health
by email.

The storms can last hours to days, and when strong enough
can disrupt satellites and push the aurora borealis much further
south than usual, as happened this winter over the United
Kingdom.

The electromagnetic upheaval also makes magnetic compasses
behave erratically and in 1989, a geomagnetic storm disrupted
the Quebec power grid, causing a blackout in the province that
lasted nine hours.

Researchers aren't sure, however, why the storms would be
linked to stroke risk.

The review cites six large stroke studies including a total
of more than 11,000 patients that took place between 1981 and
2004 in Europe, Australia and New Zealand.

Feigin and his colleagues considered the dates of each
participant's first stroke alongside a record of geomagnetic
activity from the same time period from the U.S. National
Oceanic and Atmospheric Administration.

For each incident of stroke, researchers compared
geomagnetic activity that day with activity on eight other days
when the patient did not have a stroke.

According to their results, which are published in the
journal Stroke, geomagnetic storms were 19 percent more likely
to occur on geomagnetic storm days than on other days.

That is a fairly significant increase in risk, Feigin said,
comparing it to the stroke risk associated with taking hormone
replacement therapy.

On average, people suffered strokes around age 70, but the
connection to geomagnetic storms was stronger for people under
age 65.

Over the course of the study, geomagnetic activity didn't
change much from year to year, but it was calmest from 1996 to
1998, which was the period of solar minima in the sun's 11-year
activity cycle, when solar flares and sunspots are least common.

Feigin pointed out that 2014 is a "solar maximum" year.

"There is preliminary evidence suggesting effects of
geomagnetic storms on blood pressure increase, variations of
heart rhythm and blood clotting abilities, all of which are
known risk factors for stroke," Feigin said, although that's
mostly conjecture at this point.

Earth's magnetic field differs depending on where you are on
the planet, but geomagnetic storms influence the whole magnetic
field, and based on this review they seem to affect stroke risk
in Europe and Australasia in the same way, he said.

"It's a fascinating idea, at least on that level," said Dr.
James Brorson, an expert in the evaluation and treatment of
stroke in the University of Chicago department of neurology. "I
wasn't aware that this was even postulated."

A 19 percent increase in stroke risk is enough to make one
sit up and take notice, but not as large as the risk increase
due to smoking or high blood pressure, he said.

"The idea that geomagnetic storms influence whether or not
we have a stroke almost seems like magical thinking," he said,
and it's certainly too early for people to change their behavior
based on the storms.

"Any patient of mine, I would counsel them to by no means
worry about this," Brorson told Reuters Health by phone. "It
remains to be seen whether this holds up."

Besides, he said, geomagnetic storms are not usually very
predictable, and even if they were, there's really nothing
anyone can do to avoid them. The Earth's magnetic field is
everywhere, indoors and out.

Although the authors of the review suggest that people at
risk for stroke could take extra precautions in magnetically
turbulent times, like avoiding stress, excessive alcohol and
dehydration, those are measures people should be taking all the
time anyway, Brorson said.